1. Field of the Invention
This invention relates generally to electronic devices, and more particularly to a device for mounting an image sensor. Even more particularly, the invention relates to a device for mounting an image sensor on a flexible substrate such as a flexible printed circuit (FPC).
2. Description of the Background Art
Unlike traditional cameras that use film to capture and store an image, digital cameras use various solid-state devices collectively referred to as image capture devices. These small silicon chips contain millions of photosensitive diodes called photosites. When the shutter (mechanical or electrical) is open, each photosite records the intensity or brightness of the incident light by accumulating a charge; the more light, the higher the charge. The brightness recorded by each photosite is then stored as a value indicative of the brightness and/or color for a corresponding pixel of the captured image. The brightness/color values can then be used to set the colors and brightness of dots on a display screen or ink on a printed page to reconstruct the image.
Image capture devices are mounted within digital cameras so as to be aligned with a lens and an opening in the camera body. The silicon chip (die) itself is typically mounted onto a ceramic leadless chip carrier (CLCC), which in turn is mounted on a printed circuit board (PCB). The CLCC is made of a ceramic material which can withstand high temperatures to withstand the soldering of electrical connections. It does not have leads but has one set of contact pads around it's perimeter for making electrical connections to the PCB via a reflow solder process and another set of contact pads or lead frame for making electrical connections (e.g., via wire bonding) with the die. During the mounting process, the contact pads of the CLCC are connected (e.g., via soldering) to electrical plated pads of the PCB. A lens is then mounted to the PCB over the die and CLCC. Finally, the PCB is mounted in a fixed position within the camera, so that the lens aligns with an opening in the camera.
The devices and assembly methods of the prior art have several disadvantages in both the manufacturing process and the quality of the device. Alignment of the image capture device with the opening in the camera can be difficult, particularly in small cameras (e.g., cameras in mobile telephones). Because multiple devices are mounted on the PCB, the tolerances accumulate to reduce the precision with which the image capture device can be aligned with the opening. Additionally, PCBs typically include other components (e.g., keypad, etc.) that must be aligned with other openings, further complicating the alignment problem.
FIG. 1 illustrates one example of a prior art solution to the above-described alignment problem. In this particular embodiment, a camera device 100 includes an independent camera module 102, which is flexibly coupled to a main PCB 108. Independent camera module 102 includes a PCB 106 that supports a CLCC 104, which in turn supports a die 114. PCB 106 is connected to a main PCB 108 via a flexible electrical circuit 120 that transfers data/power between the independent camera module PCB 102 and main PCB 108. The FPC 120 decouples the physical alignment of independent camera module 102 and main PCB 108.
Although the device of FIG. 1 helps alleviate the alignment problem, it creates other disadvantages. For example, camera module 100 requires more components than the previously described embodiment, such as FPC 120 and an additional PCB 106. Further, the additional components require additional assembly steps. The cost of the additional components and the additional assembly steps increase the overall cost of the product.
Note also that camera module 100 includes an increased number of electrical connections and, therefore, has an increased number of points of possible failure. In particular, camera module 100 includes at least four sets of electrical connections. A first set of electrical connections 112 exist between die 114 and CLCC 104. A second set of electrical connections 113 exist between CLCC 104 and PCB 106. A third set of electrical connections (inside connector 136) exist between PCB 106 and FPC 120. Finally, a fourth set of electrical connections (inside connector 138) exist between FPC 120 and main PCB 108. The increased number of electrical connections, and thus the increased number of points of possible failure, decreases the overall reliability of the product.
What is needed, therefore, is a device that helps alleviate the alignment problem, yet requires fewer components than prior art solutions. What is also needed is a device that helps alleviate the alignment problem, yet includes fewer electrical connections (e.g., solder points, etc.), and thus fewer points of possible failure, as compared to the prior art solutions. What is also needed is a device that requires fewer manufacturing steps and/or a shorter assembly time as compared to the prior art.